Funds are requested for 80% of the cost of purchasing a matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometer. The 5 primary users and 8 secondary users of this instrument would be from the Department of Biochemistry at the University of Wisconsin-Madison. Other users would be from laboratories of the approximately 750 faculty members performing biomedical research at the university. Currently, the University of Wisconsin-Madison campus has only one MALDI-TOF mass spectrometer. This instrument is saturated with other users and, located 1/4-mile away in the chemistry department, is not readily accessible to the primary and secondary users. The 13 primary and secondary users of the requested instrumentation are NIH-funded investigators who study biomolecules and their interactions. They have active collaborations, routinely share equipment and ideas, and participate in common training and degree programs. The major users of the instrumentation would be the 90 students and staff working in the laboratories of the primary users. The MALDI-TOF mass spectrometer would be placed in the existing campus Biophysics Instrumentation Facility, which is located in the Department of Biochemistry. There, the mass spectrometer would join other state-of- the-art instruments for characterizing biomolecules and their interactions. This facility is managed by a full-time Instrumentation specialist, who would oversee the day-to-day use and maintenance of the mass spectrometer. It is anticipated that students and staff would obtain their own MALDI-TOF mass spectra after a short training session from the Instrumentation Specialist.